This invention relates to a cellular radio system and particularly to efficient utilization of its capacity.
In prior art cellular radio system base stations are arranged in such a way that the geographical areas they cover usually overlap to some extent. Therefore mobile stations located in the border areas of the coverage areas of the base stations usually can select among several alternative base stations the one offering the best audibility. For practical reasons, however, the aim is to arrange adjacent base stations in such a way that their overlapping coverage area is as small as possible. This allows a geographical area of a maximum size to be covered with a minimum number of base stations.
The overlapping coverage area of adjacent base stations being as small as possible has, however, caused problems. For instance, in the border areas of the base station coverage areas there can be shadow regions where the audibility of the system is poor. A further problem is that the traffic capacity of one of the two adjacent base stations can be fully reserved, while the other can still have plenty of free traffic capacity available. In this case a mobile station trying to contact the fully reserved base station is not able to establish a telecommunication connection, unless it happens to be located in the overlapping (as small as possible) coverage area of the base stations where both base stations are audible. In order to enable the traffic load to be more efficiently divided between the base stations, it would therefore be advantageous that the overlapping coverage area of adjacent base stations would be as large as possible, whereby as many mobile stations as possible could select the base station among a plural number of base stations audible at the point concerned. This would, however, significantly increase the price of the system because more base stations would need to be built within an area of a specific size.